The collective nature of legislating forces legislators to rely on one another for information and support. This collaborative activity requires a choice about partnerships in an environment of uncertainty. The basic size and organization of a legislature amplifies this uncertainty in relational choices. Analysis of collaborative patterns between all the U.S. state legislators in 2007 corroborates this expectation, indicating that large legislatures have highly partisan collaborative networks with generally low density, while larger legislative committees mitigate these effects. Thus, even when the attributes of legislators do not change, the organizational size of the legislature can shape how those legislators interact.